Topic Contents

Lumbar Puncture

Test Overview

A lumbar puncture (also called a spinal
tap) is a procedure to collect and look at the fluid (cerebrospinal fluid, or CSF) surrounding the brain and spinal cord.

During a
lumbar puncture, a needle is carefully inserted into the spinal canal low in
the back (lumbar area). Samples of CSF are collected. The samples are studied
for color, blood cell counts, protein, glucose, and other substances. Some of
the sample may be put into a special culture cup to see if any infection, such
as bacteria or
fungi, grows. The pressure of the CSF also is measured
during the procedure.

Measure the
pressure of cerebrospinal fluid (CSF) in the space surrounding the spinal cord.
If the pressure is high, it may be causing certain symptoms.

A lumbar puncture may also be done to:

Put
anesthetics or medicines into the CSF. Medicines may
be injected to treat
leukemia and other types of cancer of the central
nervous system.

Put a dye in the CSF that makes the spinal cord and
fluid clearer on X-ray pictures (myelogram).
This may be done to see whether a disc or a cancer is bulging into the spinal
canal.

In rare cases, a lumbar puncture may be used to lower the
pressure in the brain caused by too much CSF.

How To Prepare

Before you have a lumbar puncture, tell
your doctor if you:

Are taking any medicines. If you take medicines
every day, ask your doctor whether you should take these medicines on the day
of the lumbar puncture.

Are allergic to any medicines, such as
those used to numb the skin (anesthetics).

Have had
bleeding problems or take blood-thinners, such as aspirin or warfarin
(Coumadin).

Are or might be pregnant.

Take any herbal
remedies. Some of these remedies may thin the blood.

You will empty your bladder before the procedure.

For a lumbar puncture, you will be asked to sign a consent form. Talk to
your doctor about any concerns you have regarding the need for the procedure,
its risks, how it will be done, or what the results will mean. This procedure
is often done in an emergency situation. If you are scheduled to have this
procedure, you can understand the importance of it by filling out the
medical test information form(What is a PDF document?)
.

How It Is Done

A lumbar puncture may be done in your
doctor's office, in an emergency room, or at your bedside in the hospital. It
may also be done in the radiology department if
fluoroscopy is used.

You will lie on a
bed on your side with your knees drawn up toward your chest. Or you may sit on
the edge of a chair or bed and lean forward over a table with your head and
chest bent toward your knees. These positions help widen the spaces between the
bones of the lower spine so that the needle can be inserted more easily. If
fluoroscopy is used, you will lie on your stomach so the fluoroscopy machine
can take pictures of your spine during the procedure. See a picture of a
lumbar puncture.

Your doctor marks your lower back (lumbar area)
with a pen where the puncture will occur. The area is cleaned with a special
soap and draped with sterile towels. A numbing medicine (local anesthetic) is
put in the skin.

Then a long, thin needle is put in the spinal
canal. When the needle is in place, the solid central core of the needle
(stylet) is removed. If the needle is in the right spot in the spinal canal, a
small amount of cerebrospinal fluid (CSF) will drip from the end of the needle.
If not, the stylet will be put back in and the needle will be moved in a little
farther or at a different angle to get to the fluid. Your doctor may need to
move to another area of your spine if it is hard to get to the spinal
fluid.

When the needle is in the spinal canal, a device called a
manometer is hooked to the needle to measure the pressure of the CSF. You may
be asked to straighten your legs while you are lying down. Your doctor takes
the pressure reading, called the opening pressure, and checks whether the fluid
is clear, cloudy, or bloody. Several small samples of fluid are collected and
sent to the lab for study.

A final pressure reading, called the
closing pressure, may be taken after the fluid samples are done. The needle is
taken out and the puncture site is cleaned and bandaged.

The
entire procedure takes about 30 minutes.

To lower your chance of
getting a headache following a lumbar puncture, you may be told to lie flat in
bed or with your head slightly raised for 1 to 4 hours. Since your brain makes
new CSF all the time and replaces it 2 to 3 times a day, the small amount of
fluid that is removed will be quickly replaced. You may be told to drink extra
fluids after the procedure to help prevent or to reduce the severity of a
headache.

How It Feels

Some people find it uncomfortable to lie
curled up on their side. The soap may feel cold on your back. You will probably
feel a brief pinch or sting when the numbing medicine is given. You may feel a
brief pain when the spinal needle is inserted or repositioned.

During the procedure, the needle may touch one of your spinal nerves and
cause a tingling feeling, like a light electrical shock, running down one of
your legs. The needle will not touch or damage the spinal cord.

Some people (10% to 25%) develop a headache after having a lumbar
puncture. Of those who do get headaches, only about half report that they are
severe. These headaches last 24 to 48 hours and go away on their own. Pain
medicine does not help control the headache, but lying flat in bed for several
hours after the procedure may help the headache.

You may feel
tired and have a mild backache the day after the procedure. Some people have
trouble sleeping for 1 to 2 days.

Risks

A lumbar puncture is generally a safe procedure.
In some cases, a leak of cerebrospinal fluid (CSF) may develop after a lumbar
puncture. Symptoms of this problem are a headache that does not go away after 1
to 2 days. A CSF leak can be treated with a blood "patch," in which the
person's own blood is injected into the area where the leak is occurring in
order to seal the leak.

About 1 in 1,000 people who have a lumbar
puncture have a minor nerve injury. This heals on its own with time. There is
also a small chance of infection of the CSF (meningitis), bleeding inside the
spinal canal, or damage to the cartilage between the vertebrae. Your doctor
will talk with you about these risks.

People who have bleeding
problems and those who are taking blood-thinning medicine (such as warfarin or
heparin) have a higher chance of bleeding after the procedure. A lumbar
puncture may not be done unless it is needed for a life-threatening
illness.

A lumbar puncture may cause serious problems for people
who have high pressure in the brain caused by a tumor, a pocket of infection in
the brain (abscess), or major bleeding inside the brain. Your
doctor will check your nervous system, spinal cord and brain before doing a
lumbar puncture. In some cases, a
computed tomography (CT) scan or
magnetic resonance imaging (MRI) scan may be done
before the lumbar puncture to know that it is safe to do the puncture.

After the procedure

Call your doctor immediately
if you have:

Chills or a fever.

A stiff neck.
This may be a sign of a developing infection.

Any drainage or
bleeding from the puncture site.

A severe
headache.

Any numbness or loss of strength below the puncture
site.

Results

A
lumbar puncture (also called a spinal tap) is a procedure to collect and look
at the fluid (cerebrospinal fluid, or CSF) surrounding the brain and
spinal cord. Many different tests can be done on the CSF. Some results will be
ready right away, some will take a few hours after the procedure, and others
will take several weeks.

Normal results

Appearance:

CSF is normally
clear and colorless.

Pressure:

Normal CSF pressure in the
lower back for an adult ranges from 50–180 millimeters (mm) water. For
children, the normal opening pressure range is 10–100 mm water.

Protein:

The normal protein content of
CSF in an adult's lower back (lumbar) region is 15–45
milligrams per deciliter (mg/dL) or less. Older adults
and children may have higher values (up to 70 mg/dL) that are still in the
normal range.

Glucose:

The normal range for glucose
content in the CSF is at least 40%–80% of the blood glucose level. The levels
may be slightly increased if the person has just eaten.

No infectious organisms (such
as bacteria, fungi, or a virus) are found in the CSF sample. No tumor cells are
present.

Abnormal results

Appearance:

Blood in the CSF
can result from bleeding (hemorrhage) in or around the spinal cord or brain,
but it may also be caused by tiny blood vessel poked during the spinal tap. If
a brain hemorrhage has occurred, the color of the CSF may change from red to
yellow to brown over several days. Bleeding caused by the lumbar puncture
itself will show more red blood cells in the first sample collected than in
later samples. Cloudy CSF may mean an infection (such as
meningitis or a brain
abscess) is present.

Pressure:

High CSF pressure may occur as
a result of swelling (edema) or bleeding (hemorrhage) in the brain, infection
(such as meningitis),
stroke, or other circulatory problems. Below-normal
pressure may mean a blocked spinal canal.

Low glucose levels in the CSF
are abnormal and may be caused by bacterial meningitis. Viral meningitis does
not often cause low glucose levels in the CSF. Brain hemorrhage may also cause
low glucose levels several days after bleeding begins. Higher-than-normal
glucose levels are often caused by diabetes.

Antibodies,
bacteria, or other organisms in the CSF means that an infection (such as
syphilis) or disease is present. Bacterial markers
(bacterial
antigens) that show up mean meningitis. Cultures or
stains of the CSF may also help show the cause of meningitis or
encephalitis.

Your doctor may order other special tests on the CSF fluid
depending on your symptoms and medical history.

What Affects the Test

Reasons you may not be able to
have the biopsy or why the results may not be helpful include:

Not being able to lie still during the
procedure.

Having conditions such as
obesity,
dehydration, spinal disease, severe
arthritis, or recent spinal surgery. These conditions
may make it hard to do a lumbar puncture with the person lying down. The
procedure may need to be done with the person sitting up and bent forward. In
some cases, the procedure may need to be done with a special X-ray method
called
fluoroscopy. This is used to guide the placement of
the spinal needle.

Bleeding into the cerebrospinal fluid (CSF). The
needle puncture can cause bleeding into the CSF. Several samples of the fluid
can show the difference between bleeding from the puncture and bleeding caused
by a brain hemorrhage.

Not being able to collect a sample of the
fluid. This is called a "dry tap."

A skin
infection on the lower back. Doing a lumbar puncture in this case may allow the
infection to spread into the spinal canal.

Bleeding disorders,
which may increase the chance of bleeding during the procedure.

Other tests that may be done include:

A cisternal or ventricular puncture.
Cerebrospinal fluid (CSF) can be collected from the upper spinal canal at the
base of the skull (cisternal puncture) or from within the skull (ventricular
puncture) when it is not possible to get CSF from the lumbar area. These
procedures are done by a trained
radiologist or neurosurgeon. Special X-ray methods are
used to guide the placement of the needle.

Bacterial marker
studies. In cases of suspected bacterial meningitis, bacterial marker
(bacterial antigen) studies can quickly find the common types of bacteria that
cause meningitis. Antibiotic treatment for that bacteria can be started
immediately.

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